Systems and methods for tuning propeller noise

ABSTRACT

The present disclosure relates to devices, systems, and methods for controlling and/or augmenting acoustic sounds emitted from flight vehicles, such as unmanned aerial vehicles (UAVs). For example, while in flight, a UAV may emit a characteristic sound or tone (or a plurality of such tones), which may be a result of propeller and/or motor noise. To mitigate such noise from UAVs, disclosed embodiments may include acoustic resonators that may provide additional tones to complement the sounds or tones emitted from the UAV. Namely, the acoustic resonators may be shaped, adjusted, or otherwise controlled to emit additional tones that form pleasing intervals in combination with the characteristic tone(s) from the UAV.

PRIORITY CLAIM

This application claims priority to Provisional Application No.62/331,383 filed on May 3, 2016, herein incorporated by reference in itsentirety.

BACKGROUND

Unmanned autonomous vehicles (UAVs), helicopters, and otherpropeller-driven vehicles take advantage of rotating propeller blades toprovide thrust and/or lift for movement. The high rotational speed ofthe propeller blades typically causes them to emit a characteristic“drone” or whine, which may be displeasing to listeners.

Musical chords include a plurality of tones consisting of one or moreintervals. Chords may have pleasing (consonant) or displeasing(dissonant) properties with listeners based on the intervals includedwithin the respective chord. For example, major chords that include amajor third and a perfect fifth interval may sound “happy” or“complete.” Conversely, a minor chord that may include a minor third anda perfect fifth may be considered “sad” or “blue.”

SUMMARY

Systems and methods disclosed herein relate to modifying an acousticenvironment around a propeller-driven vehicle. Namely, the propellers ofsuch vehicles may emit an undesirable whine or drone noise when inoperation. The natural drone noise may have a least one fundamentaltone. In such a scenario, an acoustic resonator may emit an additionaltone that may form an interval, such as a major third or a perfect fifthwith the fundamental tone. In some embodiments, one or more acousticresonators may provide a major chord or a melody to help augment thenatural noise of the propeller-driven vehicle. As such, the systems andmethods describe herein may help reduce undesirable noise pollution frompropeller-driven vehicles, such as unmanned aerial vehicles (UAVs).

In an aspect, a device is provided. The device includes at least onepropeller. While rotating, the at least one propeller emits at least onetone. The device also includes at least one acoustic resonator proximateto the at least one propeller. The at least one acoustic resonator isconfigured to emit at least one additional tone. The at least oneadditional tone forms an interval with respect to the at least one tone.The interval includes a major third or a fifth.

In an aspect, a system is provided. The system includes at least onepropeller and at least one acoustic resonator proximate to the at leastone propeller. The system also includes at least one tuning elementcoupled to the at least one acoustic resonator and at least one sensor.The system additionally includes a controller including at least oneprocessor and a memory. The at least one processor is configured tocarry out instructions stored in the memory so as to perform operations.The operations include receiving, via the at least one sensor,information indicative of at least one tone emitted from the at leastone propeller. The operations also include, based on the receivedinformation, adjusting the at least one tuning element such that theadjusted tuning element and the corresponding acoustic resonator emit atleast one additional tone.

In an aspect, a method is provided. The method includes causing at leastone propeller to rotate. At least one acoustic resonator is proximate tothe at least one propeller. At least one tuning element is coupled tothe at least one acoustic resonator. The method also includes, while theat least one propeller is rotating, receiving, via at least one sensor,information indicative of at least one tone emitted from the at leastone propeller. The method additionally includes, based on the receivedinformation, adjusting the at least one tuning element such that theadjusted tuning element and the corresponding acoustic resonator emit atleast one additional tone.

In an aspect, a system is provided. The system includes various meansfor carrying out the operations of the other respective aspectsdescribed herein.

These as well as other embodiments, aspects, advantages, andalternatives will become apparent to those of ordinary skill in the artby reading the following detailed description, with reference whereappropriate to the accompanying drawings. Further, it should beunderstood that this summary and other descriptions and figures providedherein are intended to illustrate embodiments by way of example onlyand, as such, that numerous variations are possible. For instance,structural elements and process steps can be rearranged, combined,distributed, eliminated, or otherwise changed, while remaining withinthe scope of the embodiments as claimed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a schematic diagram of a system, according to anexample embodiment.

FIG. 2A illustrates an aircraft, according to an example embodiment.

FIG. 2B illustrates an aircraft, according to an example embodiment.

FIG. 2C illustrates an aircraft, according to an example embodiment.

FIG. 2D illustrates an aircraft, according to an example embodiment.

FIG. 3A illustrates a propeller assembly, according to an exampleembodiment.

FIG. 3B illustrates propeller assemblies, according to exampleembodiments.

FIG. 3C illustrates a propeller assembly and resonator, according to anexample embodiment.

FIG. 4A illustrates various musical chords, according to an exampleembodiment.

FIG. 4B illustrates an acoustic spectrum, according to an exampleembodiment.

FIG. 5 illustrates a method, according to an example embodiment.

DETAILED DESCRIPTION

Example methods, devices, and systems are described herein. It should beunderstood that the words “example” and “exemplary” are used herein tomean “serving as an example, instance, or illustration.” Any embodimentor feature described herein as being an “example” or “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments or features. Other embodiments can be utilized, and otherchanges can be made, without departing from the scope of the subjectmatter presented herein.

Thus, the example embodiments described herein are not meant to belimiting. Aspects of the present disclosure, as generally describedherein, and illustrated in the figures, can be arranged, substituted,combined, separated, and designed in a wide variety of differentconfigurations, all of which are contemplated herein.

Further, unless context suggests otherwise, the features illustrated ineach of the figures may be used in combination with one another. Thus,the figures should be generally viewed as component aspects of one ormore overall embodiments, with the understanding that not allillustrated features are necessary for each embodiment.

I. Overview

The present disclosure relates to devices, systems, and methods forcontrolling and/or augmenting acoustic sounds emitted from flightvehicles, such as unmanned aerial vehicles (UAVs). For example, while inflight, a UAV may emit a characteristic sound or tone (or a plurality ofsuch tones), which may be a result of propeller and/or motor noise. Tomitigate such noise from UAVs, disclosed embodiments may includeacoustic resonators that may provide additional tones to complement thesounds or tones emitted from the UAV. Namely, the acoustic resonatorsmay be shaped, adjusted, or otherwise controlled to emit additionaltones that form intervals with the characteristic UAV tone(s). In anexample embodiment, the additional tones may form a major chord (e.g.,root note, major third, perfect fifth). Major chords may be used as theygenerally form a “happy” combination of tones. However, other chords arepossible. Alternatively or additionally, the additional tones may becombined together and/or successively to form a melody or song.

By adding one or more additional tones to form intervals, chords, and/ormelodies, UAVs in flight may be able to produce sounds that are lessacoustically offensive than a characteristic “drone” noise. In someembodiments, the one or more additional tones may provide an indicationof a flight mode of the UAV and/or a purpose of the UAV.

In an example embodiment, a device may include a propeller and anacoustic resonator. The propeller may emit a tone while rotating. Theacoustic resonator may be arranged proximate to the propeller. Forexample, the acoustic resonator may be a shroud that partially enclosesthe propeller. The acoustic resonator may alternatively be coupled tothe propeller and/or form a portion of the shroud. The acousticresonator may be shaped or otherwise configured to emit at least oneadditional tone such that the natural UAV tone and the additionaltone(s) form a chord. The chord may include a plurality of intervalsthat includes a major third and a perfect fifth with respect to thenatural UAV tone.

In another example embodiment, a system may further include at least onetuning element coupled to the acoustic resonator, a sensor, and acontroller having a processor and a memory. The controller may carry outcommands such as receiving, via the sensor, information about the toneor tones emitted from the propeller. Based on the information, thecontroller may adjust the at least one tuning element, which in turn maycause the acoustic resonator to emit an additional tone or tones.

In a further example embodiment, a method may include causing apropeller to rotate. An acoustic resonator may be proximate to thepropeller and the acoustic resonator may be coupled to at least onetuning element. While the propeller is rotating, the method may includereceiving information from a sensor. The information may be indicativeof a tone or plurality of tones produced by the spinning propellerblade(s). Based on the information, the method may include adjusting theat least one tuning element so the adjusted tuning element and thecorresponding acoustic resonator emit at least one additional tone. Asdescribed herein, the at least one additional tone may include a melody,an interval, and/or a chord.

II. Example Devices and Systems

FIG. 1 illustrates a schematic diagram of a system 100, according to anexample embodiment. System 100 includes a propeller 110, an acousticresonator 120, and a tuning element 130. System 100 also includes asensor 140 and a controller 150. Generally, system 100 may beincorporated in an unmanned aerial vehicle (UAV) or another type ofpropeller-driven vehicle, such as a helicopter, propeller-drivenairplane, hovercraft, or airboat. Alternatively, system 100 may beincorporated into other types of vehicles or applications that utilizepropellers, such as wind turbines, open rotor (propfan), turboprop, orturbofan engines.

Propeller 110 may be operable to provide thrust, lift, and/or propulsionfor a vehicle, such as a UAV or another propeller-driven vehicle.Propeller 110 may be one of a plurality of propellers. Propeller 110 mayinclude any number of propeller blades. For example, in an embodiment,propeller 110 may include a single propeller blade. Alternatively,propeller 110 may include two or more propeller blades. In some exampleembodiments, propeller 110 may include a shroud that surrounds and/or isproximate to at least a portion of a path of the rotating propeller.That is, the shroud may include an enclosure that at least partiallyencloses the propeller 110.

Propeller 110 is configured to rotate to provide propulsion, for examplein the case of an airplane propeller. Additionally or alternatively,propeller 110 may provide electrical power, such as in the case of awind turbine or hybrid propeller drive. While rotating, propeller 110may emit one or more “natural tones” that may vary based on, forexample, a rotational rate (RPM), airspeed, aircraft configuration, etc.In an example embodiment, propeller 110 may be configured to rotate at3000 RPM during normal cruise operation. In such a scenario, propeller110 may emit a natural tone around 120 Hz and corresponding overtones(e.g., 240 Hz, 360 Hz, 480 Hz, etc.).

Acoustic resonator 120 may include one or more elements configured toform one or more tones based, at least in part, on a natural resonanceof acoustic resonator 120. Acoustic resonator 120 may include one ormore pipes, which may have different length sections, similar to a pipeorgan. Acoustic resonator 120 may be incorporated into a shroud ofpropeller 110. For example, acoustic resonator 120 may be a cavityresonator that may emit sound in response to air vibrating in a cavityof the shroud. In an example embodiment, acoustic resonator 120 may becoupled to propeller 110. Additionally or alternatively, acousticresonator 120 may be located elsewhere on the aircraft/vehicle. In anembodiment, system 100 may include a plurality of acoustic resonators,which may be arranged along different radii of the propeller. In such ascenario, the position of the respective resonators may be arrangedalong propeller 110 so their relative speeds during normal propelleroperation provide different respective wind speeds across them. As such,each of the plurality of acoustic resonators may provide a differenttone of a collective chord.

Acoustic resonator 120 may include a resonating device such as those inmusical instruments. For example, acoustic resonator 120 may be similaror identical to strings of a stringed instrument, a head of a drum, orwooden or steel bars on another type of percussion instrument, such as axylophone. Generally, acoustic resonator 120 may be formed of metal,plastic, wood, or another type of material configured to sustain andproject vibrations and/or standing waves associated with acoustic tonesdescribed herein. Other types of acoustic resonators are contemplatedwithin the scope of this disclosure.

Acoustic resonator 120 may produce tones with various timbres, or tonequalities. For example, acoustic resonator 120 may produce tones withspecific attack and sustain characteristics. Additionally oralternatively, acoustic resonator 120 may produce tones with acharacteristic spectral envelope or characteristic prefix (onset ofsound). In some embodiments, a timbre of acoustic resonator 120 may becontrolled via tuning element 130.

Tuning element 130 may be operable to adjust acoustic resonator 120. Forexample, tuning element 130 may be operable to adjust acoustic resonator120 such that acoustic resonator 120 may controllably emit a first toneor a second tone. That is, tuning element 130 may be controlled tochange one or more tones, or the pitch of such tones, emitted byacoustic resonator 120. By way of example, tuning element 130 may beconfigured to adjust one or more resonance frequencies of acousticresonator 120. In an example embodiment, tuning element 130 may includea movable portion of the acoustic resonator 120, e.g., a valve ormovable cavity extension. That is, tuning element 130 may resemblecontrollable valves on a flute or saxophone. Alternatively oradditionally, tuning element 130 may be operable to expand or compress aresonant cavity of acoustic resonator 120. That is, tuning element 130may resemble and/or operate similarly to a trombone or slide whistle,although other configurations are, of course, possible.

Sensor 140 may include an acoustic sensor configured to provideinformation indicative of acoustic tones within an environment of system100. In an example embodiment, sensor 140 may be configured to providereal-time information indicative of the tonal content of the environmentof system 100. For example, sensor 140 may provide information to thecontroller 150 about the audio spectrum. Specifically, sensor 140 may beconfigured to detect various aspect of sound (e.g., volume, tone, andtimbre) produced by propeller 110 and/or acoustic resonator 120. In anexample embodiment, sensor 140 may include one or more microphones.Additionally or alternatively, sensor 140 may include an accelerometeror another type of transducer configured to detect mechanical oracoustic vibrations. Other types of sensors are contemplated herein.

Sensor 140 may alternatively be configured to provide informationregarding a rotational speed of propeller 110 (e.g., revolutions perminute, RPM). In such a scenario, sensor 140 may include a timing light,a timing camera, a photodetector, and/or another system or deviceconfigured to provide information indicative of a movement of propeller110. Based on the information from sensor 140, controller 150 may beoperable to determine properties of sound being emitted from thepropeller 110 and/or acoustic resonator 120. For example, controller 150may use a look-up table with a plurality of acoustic spectra measuredunder similar propeller speed conditions.

Controller 150 includes at least one processor 152 and a memory 154.Controller 150 may include one or more computers configured to carry outoperations. For example, the at least one processor 152 may executeinstructions stored in memory 154 so as to conduct the operations. Atleast one processor 152 may include a multi-core processor or adistributed server system. Memory 154 may include a non-transitorycomputer readable medium, such as a dynamic random access memory (DRAM).Other types of computer readable media are contemplated.

Controller 150 may be located proximate to one or more elements ofsystem 100. Alternatively or additionally, at least a portion ofcontroller 150 need not be located proximate to other elements of system100. For example, controller 150 may include a plurality of computerssuch as a cloud server network.

Controller 150 may carry out various operations, such as receiving, viasensor 140, information indicative of at least one tone emitted frompropeller 110. That is, sensor 140 may provide acoustic information tocontroller 150, which may include volume, tone, pitch, etc.

Based on receiving the information, controller 150 may adjust tuningelement 130. For example, controller 150 may cause a valve of tuningelement 130 to close, open, or otherwise change position. Alternativelyor additionally, controller 150 may cause a resonant cavity of acousticresonator 120 to become smaller, larger, or otherwise change shape.

In such a scenario, acoustic resonator 120 may emit at least one tone inaddition to the natural tone(s) emitted from propeller 110 duringoperation. In particular, the natural tone(s) emitted from propeller 110during operation in combination with the at least one further toneemitted from the acoustic resonator 120 may include at least oneinterval. The at least one interval may include a major third, perfectfifth, or another interval. The respective intervals may be consideredwith respect to one or more natural tones emitted from propeller 110. Assuch, the one or more natural tones may be a considered “root” orfundamental tone. Additionally or alternatively, one or more furthertones emitted from acoustic resonator 120 may be considered the “root”or fundamental tone. Furthermore, chord inversions are contemplated. Assuch, a fundamental tone may be provided by acoustic resonator 120. Inan example embodiment, the combination of natural tones and furthertones may form a pleasant chord, such as a major chord.

It will be understood that many different pleasant-sounding chords,tones, and/or timbres are possible. Additionally or alternatively,system 100 may be configured to emit a melody, harmony, or another typeof succession of tones. Furthermore, system 100 may be configured toemit sounds based on an operating state of the vehicle.

FIGS. 2A-2D illustrate various example aircraft, according to exampleembodiments. System 100 may be integrated into such example aircraft asillustrated and described in FIG. 1. However, system 100 may beintegrated into other vehicles or applications as well.

FIG. 2A illustrates an aircraft 200, according to an example embodiment.Aircraft 200 may be a UAV with one or more propellers 202. Asillustrated, propeller 202 may include two propeller blades, howeverother numbers of propeller blades are contemplated. While rotating,propeller(s) 202 may be configured to provide lift and/or thrust foraircraft 200. The propellers 202 may be surrounded, at least in part, bya cowling or a shroud 204. In some embodiments, shroud 204 may form partof a ducted propeller assembly, such as a Kort nozzle. For example, aposition and/or angle of shroud 204 and propeller 202 may be adjusted soas to control a position, speed, and/or heading of aircraft 200 while inflight. In an embodiment, acoustic resonator(s) 120 and/or tunableelement(s) 130 may be incorporated into shroud 204, propellers 202, orelsewhere as elements of aircraft 200.

In an example embodiment, aircraft 200 may include landing gear 206,which may include one or more legs, floats, and/or wheels. Aircraft 200may also include a payload container 208 configured to house a payload.For example, aircraft 200 may be configured to autonomously deliverpayloads to various locations. Alternatively or additionally, aircraft200 may be configured to monitor traffic or weather conditions.

FIG. 2B illustrates an aircraft 210, according to an example embodiment.Aircraft 210 may include one or more propellers 212 and flight surfaces214. In an embodiment, acoustic resonator(s) 120 and/or tunableelement(s) 130 may be incorporated into propellers 212 and/or flightsurfaces 214.

FIG. 2C illustrates an aircraft 230, according to an example embodiment.Aircraft 230 may include at least one propeller 232. In someembodiments, aircraft 230 may include one or more adjustable nacelles234. In such a scenario, acoustic resonator(s) 120 and/or tunableelement(s) 130 may be incorporated into the at least one propeller 232or the one or more adjustable nacelles 234. In example embodiments,aircraft 200, aircraft 210, and aircraft 220 may be configured forvertical takeoff and landing (VTOL).

FIG. 2D illustrates an aircraft 240, according to an example embodiment.Aircraft 240 may include one or more propellers 242. In an embodiment,acoustic resonator(s) 120 and/or tunable element(s) 130 may beincorporated into propeller 242.

FIGS. 3A-3C illustrate various propeller assemblies, according toseveral example embodiments.

FIG. 3A illustrates a propeller assembly 300, according to an exampleembodiment. Propeller assembly 300 includes a propeller 302 and a shroud304. The shroud 304 may be coupled to the propeller 302 and itsrotational axis 308 via one or more struts 306.

Shroud 304 may include a fairing, a nacelle, or another type of housingthat at least partially encloses propeller 302. Shroud 304 may beaerodynamically shaped and/or may be configured to change shape tocontrol, for example, a vector/direction of thrust.

In an example embodiment, shroud 304 may be configured to change itsdepth 310 with respect to the axis of rotation 308. Additionally oralternatively, shroud 304 may be configured to adjust its radius 312,diameter, and/or circumference with respect to the axis of rotation 308.In such a scenario, adjusting depth 310 and/or radius 312 may be similaror identical to adjusting tuning element 130 as illustrated anddescribed in reference to FIG. 1.

In an example embodiment, propeller assembly 300 may include sensor 314.Sensor 314 may be mounted to shroud 304 or another location on propellerassembly 300 or the vehicle generally. Sensor 314 may be similar oridentical to sensor 140 as illustrated and described in relation toFIG. 1. Specifically, sensor 314 may be configured to provideinformation indicative of a sound environment of the propeller assembly300. As such, sensor 314 may provide information about tones emittedfrom the propeller 302 during operation as well as tones emitted fromone or more acoustic resonators as described elsewhere herein.

FIG. 3B illustrates propeller assemblies 320, 330, and 340, according toexample embodiments. Propeller assembly 320 may include one or moreports 322 in shroud 304. As illustrated, a plurality of ports 322 may bearranged around shroud 304 and may form holes that may permit air topass from an exterior of shroud 304 to an interior of shroud 304. Assuch, the air passing through, over, and/or around the ports 322 maycreate one or more tones. Furthermore, the tones provided may change inpitch, volume, and/or timbre based on the airspeed through, over, and/oraround the ports 322.

Propeller assembly 330 includes one or more ports 332 which may beadjusted via tuning element 334. As illustrated, tuning element 334 mayinclude a flap that may be controllably opened and closed via, forexample, a mechanical actuator. By adjusting a position of tuningelement 334, an opening size 336 may be changed. As such, a volume,tone, pitch, or timbre of one or more generated tones may be controlledbased on the opening size 336.

Propeller assembly 340 may include one or more ports 342. An openingsize 346 may be adjusted by changing a position or orientation of tuningelement 344. As illustrated, tuning element 344 may include a slidingelement configured to open by retracting into a portion of the shroud304 or close by extending over the port 342. The position of tuningelement 344 may be adjusted via a mechanical actuator. Similar to otherembodiments herein, a volume, tone, pitch, or timbre of one or moregenerated tones may be controlled based on the opening size 346 of port342.

FIG. 3C illustrates a propeller assembly 350 and an acoustic resonator360, according to an example embodiment. Propeller assembly 350 mayinclude a propeller 352 and a shroud 354. One or more acousticresonators 360 may be arranged along shroud 354.

Acoustic resonator 360 may include a body 362 that defines a cavity 364.In an example embodiment, a combination of the shape and size of thecavity 364 and/or the material of body 362 may define one or moreresonant frequencies of acoustic resonator 360. Acoustic resonator 360may include a first tuning element 366 which may be configured to openand close a first port 368. Acoustic resonator 360 may also include asecond tuning element 370 configured to open and close a second port372. By opening or closing the respective ports, one or more resonantfrequencies and/or timbres produced by the acoustic resonator 360 may beadjusted. In an example embodiment, acoustic resonator 360 may include aplurality of ports which may be controllably opened or closed so as toform a chord, a note, and/or a succession of such chords or notes.Although acoustic resonator 360 is illustrated as having open ends, likea bassoon, other configurations of acoustic resonator 360 are possible.For example, acoustic resonator 360 may include one open end and oneclosed end, similar to a flute. In yet another example, acousticresonator 360 may have two closed ends. Other configurations of acousticresonator 360 for providing further tones in addition to natural tonesemitted from an operating propeller are contemplated herein.

FIG. 4A illustrates various musical chords 400, according to an exampleembodiment. The various musical chords 400 may include chords that maybe formed by the systems and methods disclosed herein. For example, inthe case of C Major, a natural tone emitted from one or more propellersmay include middle C 402, or the fundamental tone of the C Major triador chord. In such a scenario, one or more acoustic resonators may beadjusted to provide tones within the C Major chord. That is, a firstacoustic resonator may provide an E 404 above middle C 402 and a secondacoustic resonator may provide a G 406 above middle C 402. Taken incombination, the three tones may form the C Major chord.

Although C, D, E, F, G, A, and B Major chords are illustrated, it isunderstood that other chords are possible. Additionally, while triadsare illustrated, single notes, diads, and/or chords with more than threenotes are contemplated.

Furthermore, chord inversions 410 are possible. That is, the fundamentaltone or “root” of the chord need not be the lowest tone. Rather, thechords may include inverted chords that incorporate the fundamental toneat other relative positions within the chord. For example, in athree-note chord, the combination of tones may include a 1^(st)inversion chord or a 2^(nd) inversion chord. Other types of chordcombinations, such as those involving octaves and half tones arepossible.

Additionally, while major chords are described herein, other types ofchords are contemplated. For example, seventh chords 420 are possiblewithin the scope of the present disclosure. That is, the seventh chord420 may include a major triad as well as a fourth tone with an intervalof a minor seventh with respect to the fundamental tone.

FIG. 4B illustrates an acoustic spectrum 430, according to an exampleembodiment. As illustrated, acoustic spectrum 430 may include specifictones, such as C3 (130 Hz) as well as overtones (e.g., octaves) andbroad-spectrum noise. Acoustic spectrum 430 may be representative ofsounds emitted by the propeller and/or engine (solid line) as well asadditional tones produced by one or more acoustic resonators (dashedline).

Acoustic spectrum 430 includes information in the form of sound pressurelevel (SPL) in decibels (dB) versus Frequency in Hertz (Hz). In someexample embodiments, as illustrated, some propeller noise signals mayapproach 100 dB. However, such information is illustrative in natureonly and noise signals with different sound pressure levels (both louderand softer) are possible.

Acoustic spectrum 430 may be determined based on information receivedfrom a sensor, such as sensor 140 or sensor 314, as illustrated anddescribed in reference to FIGS. 1 and 3A, respectively. Based on theinformation received from the sensor, the one or more acousticresonators (e.g., acoustic resonator 120 as illustrated and described inreference to FIG. 1) may be controlled by adjusting one or more tuningelements so as to provide tones with specific intervals with respect toa natural tone, in this example C3 (130 Hz). For example, the one ormore acoustic resonators may provide tones at E3 (164.81 Hz) and G3 (196Hz). In such a scenario, a C Major chord may be provided. In otherwords, the UAV or other type of vehicle may emit a pleasing chord, whichmay be preferable to a natural “drone” sound from the propeller and/orengine.

In an example embodiment, the information received from the sensor mayindicate a change in the sound emitted from the propeller and/or theacoustic resonator(s). For example, the sound emitted from the propellermay change based on, for instance, a change of an angular rotation rateof the propeller. That is, as the propeller RPM is decreased, a toneemitted by the propeller may become lower. Furthermore, as the propellerRPM is increased, a tone emitted by the propeller may become higher.Other conditions may change the tones emitted by the propeller and/orthe acoustic resonator(s). For example, the respective tones may changebased on, for example, airspeed of the aircraft or vehicle or an angleof attack of the aircraft. In some example embodiments, the acousticresonators may be adjusted so as to compensate for such changingconditions and maintain a major chord or other successive tone pattern.

III. Example Methods

FIG. 5 illustrates a method 500, according to an example embodiment. Themethod 500 may include various blocks or steps. The blocks or steps maybe carried out individually or in combination. The blocks or steps maybe carried out in any order and/or in series or in parallel. Further,blocks or steps may be omitted from or added to method 500.

Some or all blocks of method 500 may involve elements of system 100,aircraft 200, 210, 230, or 240 and/or propeller assemblies 300, 320,330, 340, and 350 as illustrated and described in reference to FIGS. 1,2A-2D, 3A-3C, and 4A-4B. For example, some or all blocks of method 500may be carried out by controller 150 and/or processor 152 and memory154.

Block 502 includes causing at least one propeller to rotate. Forexample, in reference to FIG. 3C, the method may include causingpropeller 302 to rotate so as to provide thrust to an aircraft, such asa UAV, or another type of propeller-driven vehicle. An acousticresonator, such as acoustic resonator 360, may be located proximate tothe at least one propeller. Additionally, at least one tuning elementmay be coupled to the acoustic resonator. In an example embodiment, thetuning element could be tuning element 366 as illustrated and describedin reference to FIG. 3C. In an embodiment, the acoustic resonator mayform at least a portion of a shroud, which may include an enclosure thatat least partially encloses the propeller.

Block 504 includes, while the at least one propeller is rotating,receiving, via at least one sensor, information indicative of at leastone tone emitted from the at least one propeller. The at least onesensor may be sensor 140 or sensor 314 as illustrated and described inFIGS. 1 and 3A, respectively. Namely, the sensor may be configured toprovide information indicative of a sound spectrum of the environmentnear the propeller assembly or, more generally, the environment near theaircraft or vehicle. That is, the sensor may provide information aboutthe sounds that a person may hear while near the aircraft or vehicle.

While the propeller is rotating, the propeller may induce natural tonesbased on, for example, displacing air in a periodic fashion. The sensormay be configured to provide information about the tones producednaturally by the propeller.

Block 506 includes, based on the received information, adjusting the atleast one tuning element such that the adjusted tuning element and thecorresponding acoustic resonator emit at least one additional tone.Furthermore, a combination of the at least one additional tone and thenatural tone emitted from the propeller may form an interval. Forexample, a tuning element associated with an acoustic resonator may beadjusted such that the acoustic resonator provides one or more tones soas the combination of natural and further tones forms a major chord.Adjusting the at least one tuning element may include adjusting at leastone surface of the shroud based on a desired interval with respect tothe at least one tone.

In an example embodiment, adjusting the at least one tuning element mayinclude adjusting a resonant condition of the acoustic resonator basedon a desired interval with respect to the at least one tone. As anexample, a desired interval may include a major third, perfect fifth, oranother interval selected so as to provide given chord. In such ascenario, the chord may include a plurality of intervals with respect tothe at least one natural tone (emitted by the propeller normally). Insome embodiments, the acoustic resonator may form tones that make up amelody or harmony. For example, the melody or harmony may include aplurality of successive tones provided by the acoustic resonator. Themelody or harmony may include a well-known song, e.g., the HappyBirthday Song or Take Me Out to the Ballgame, or another characteristicmelody or harmony.

In some embodiments, the tones emitted by the acoustic resonator(s) maybe selected based on a mode of operation of the vehicle or anotherflight characteristic. For example, in the case of a UAV, a melody maybe selected from a plurality of possible melodies based on at least oneof a flight mode of the UAV, a position of the UAV, or an altitude ofthe UAV. In some embodiments, for example, an aircraft may emit a firstchord or melody during cruising flight and change to a second chord ormelody during hover and/or package delivery. Othercontextually-dependent tone/melody selections are possible.

In an example embodiment, methods and systems may provide users with anability to control tones, melodies, and/or chords emitted from theaircraft. For example, users may choose or preset tones or melodies thatare pleasing to them. In a UAV package-delivery scenario, the UAV may becontrolled to emit tones/melodies according to a preference of thedelivery recipient.

In another embodiment, methods and system may include emitting tones ormelodies based on contextual awareness. For example, while flying near abaseball stadium, the aircraft may play “Take Me Out to the Ballgame.”Additionally or alternatively, the aircraft may play an alarm tone ormelody if running out of fuel or batteries. In an example embodiment, avolume of the emitted tones and/or their content may be based on a timeof day. For example, while at night, an aircraft may decrease the volumeof emitted tones. In some embodiments, the emitted tones may be silencedor otherwise attenuated when flying over unpopulated areas. Other typesof contextual scenarios are possible.

In some embodiments, additional emitted tones may be silenced orotherwise adjusted to optimize a flight performance of the aircraft. Forexample, adjusting the emitted tones may improve battery/fuelefficiency, speed, vibration, or other flight performance measures.

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other embodiments may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anillustrative embodiment may include elements that are not illustrated inthe Figures.

A step or block that represents a processing of information cancorrespond to circuitry that can be configured to perform the specificlogical functions of a herein-described method or technique.Alternatively or additionally, a step or block that represents aprocessing of information can correspond to a module, a segment, or aportion of program code (including related data). The program code caninclude one or more instructions executable by a processor forimplementing specific logical functions or actions in the method ortechnique. The program code and/or related data can be stored on anytype of computer readable medium such as a storage device including adisk, hard drive, or other storage medium.

The computer readable medium can also include non-transitory computerreadable media such as computer-readable media that store data for shortperiods of time like register memory, processor cache, and random accessmemory (RAM). The computer readable media can also includenon-transitory computer readable media that store program code and/ordata for longer periods of time. Thus, the computer readable media mayinclude secondary or persistent long term storage, like read only memory(ROM), optical or magnetic disks, compact-disc read only memory(CD-ROM), for example. The computer readable media can also be any othervolatile or non-volatile storage systems. A computer readable medium canbe considered a computer readable storage medium, for example, or atangible storage device.

While various examples and embodiments have been disclosed, otherexamples and embodiments will be apparent to those skilled in the art.The various disclosed examples and embodiments are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims.

What is claimed is:
 1. A system, comprising: at least one propeller; atleast one acoustic resonator proximate to the at least one propeller; atleast one tuning element coupled to the at least one acoustic resonator;at least one sensor; a controller comprising at least one processor anda memory, wherein the at least one processor is configured to carry outinstructions stored in the memory so as to perform operations, theoperations comprising: receiving, via the at least one sensor,information indicative of at least one tone emitted from the at leastone propeller; and based on the received information, adjusting the atleast one tuning element such that the adjusted tuning element and thecorresponding acoustic resonator emit at least one additional tone,wherein i) the at least one tone and the at least one additional toneform a chord, wherein the chord comprises a plurality of intervals withrespect to the at least one tone, wherein the plurality of intervalscomprise at least a major third and a perfect fifth, or ii) the at leastone additional tone forms a melody, wherein the melody comprises aplurality of successive additional tones.
 2. The system of claim 1,wherein the at least one acoustic resonator forms at least a portion ofa shroud, wherein the shroud comprises an enclosure that at leastpartially encloses the at least one propeller.
 3. The system of claim 1,wherein the system is incorporated in an unmanned aerial vehicle (UAV)and wherein the at least one propeller is configured to providepropulsion for the UAV.
 4. The system of claim 1, wherein the at leastone additional tone forms an interval with respect to the at least onetone, wherein the interval comprises a major third or a fifth.
 5. Amethod, comprising: causing at least one propeller to rotate, wherein atleast one acoustic resonator is proximate to the at least one propeller,and wherein at least one tuning element is coupled to the at least oneacoustic resonator; while the at least one propeller is rotating,receiving, via at least one sensor, information indicative of at leastone tone emitted from the at least one propeller; and based on thereceived information, adjusting the at least one tuning element suchthat the adjusted tuning element and the corresponding acousticresonator emit at least one additional tone, wherein i) the at least onetone and the at least one additional tone form a chord, wherein thechord comprises a plurality of intervals with respect to the at leastone tone, wherein the plurality of intervals comprise at least a majorthird and a perfect fifth, or ii) the at least one additional tone formsa melody, wherein the melody comprises a plurality of successiveadditional tones.
 6. The method of claim 5, wherein adjusting the atleast one tuning element comprises adjusting a resonant condition of theacoustic resonator based on a desired interval with respect to the atleast one tone.
 7. The method of claim 5, wherein the at least oneacoustic resonator forms at least a portion of a shroud, wherein theshroud comprises an enclosure that at least partially encloses the atleast one propeller.
 8. The method of claim 7, wherein adjusting the atleast one tuning element comprises adjusting at least one surface of theshroud based on a desired interval with respect to the at least onetone.
 9. The method of claim 5, wherein the at least one additional toneforms an interval with respect to the at least one tone, wherein theinterval comprises a major third or a fifth.
 10. The method of claim 5,wherein the at least one propeller is configured to provide propulsionfor an unmanned aerial vehicle (UAV), wherein the method furthercomprises selecting the melody from a plurality of possible melodiesbased on at least one of a flight mode of the UAV, a position of theUAV, or an altitude of the UAV.